/*
** $Id: lutf8lib.c,v 1.16 2016/12/22 13:08:50 roberto Exp $
** Standard library for UTF-8 manipulation
** See Copyright Notice in lua.h
*/

#define lutf8lib_c
#define LUA_LIB

#include "lprefix.h"


#include <assert.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>

#include "lua.h"

#include "lauxlib.h"
#include "lualib.h"

#define MAXUNICODE  0x10FFFF

#define iscont(p)   ((*(p) & 0xC0) == 0x80)


/* from strlib */
/* translate a relative string position: negative means back from end */
static lua_Integer u_posrelat(lua_Integer pos, size_t len)
{
    if (pos >= 0) return pos;
    else if (0u - (size_t)pos > len) return 0;
    else return (lua_Integer)len + pos + 1;
}


/*
** Decode one UTF-8 sequence, returning NULL if byte sequence is invalid.
*/
static const char *utf8_decode(const char *o, int *val)
{
    static const unsigned int limits[] = {0xFF, 0x7F, 0x7FF, 0xFFFF};
    const unsigned char *s = (const unsigned char *)o;
    unsigned int c = s[0];
    unsigned int res = 0;  /* final result */
    if (c < 0x80)  /* ascii? */
        res = c;
    else
    {
        int count = 0;  /* to count number of continuation bytes */
        while (c & 0x40)    /* still have continuation bytes? */
        {
            int cc = s[++count];  /* read next byte */
            if ((cc & 0xC0) != 0x80)  /* not a continuation byte? */
                return NULL;  /* invalid byte sequence */
            res = (res << 6) | (cc & 0x3F);  /* add lower 6 bits from cont. byte */
            c <<= 1;  /* to test next bit */
        }
        res |= ((c & 0x7F) << (count * 5));  /* add first byte */
        if (count > 3 || res > MAXUNICODE || res <= limits[count])
            return NULL;  /* invalid byte sequence */
        s += count;  /* skip continuation bytes read */
    }
    if (val) *val = res;
    return (const char *)s + 1;  /* +1 to include first byte */
}


/*
** utf8len(s [, i [, j]]) --> number of characters that start in the
** range [i,j], or nil + current position if 's' is not well formed in
** that interval
*/
static int utflen(lua_State *L)
{
    int n = 0;
    size_t len;
    const char *s = luaL_checklstring(L, 1, &len);
    lua_Integer posi = u_posrelat(luaL_optinteger(L, 2, 1), len);
    lua_Integer posj = u_posrelat(luaL_optinteger(L, 3, -1), len);
    luaL_argcheck(L, 1 <= posi && --posi <= (lua_Integer)len, 2,
                  "initial position out of string");
    luaL_argcheck(L, --posj < (lua_Integer)len, 3,
                  "final position out of string");
    while (posi <= posj)
    {
        const char *s1 = utf8_decode(s + posi, NULL);
        if (s1 == NULL)    /* conversion error? */
        {
            lua_pushnil(L);  /* return nil ... */
            lua_pushinteger(L, posi + 1);  /* ... and current position */
            return 2;
        }
        posi = s1 - s;
        n++;
    }
    lua_pushinteger(L, n);
    return 1;
}


/*
** codepoint(s, [i, [j]])  -> returns codepoints for all characters
** that start in the range [i,j]
*/
static int codepoint(lua_State *L)
{
    size_t len;
    const char *s = luaL_checklstring(L, 1, &len);
    lua_Integer posi = u_posrelat(luaL_optinteger(L, 2, 1), len);
    lua_Integer pose = u_posrelat(luaL_optinteger(L, 3, posi), len);
    int n;
    const char *se;
    luaL_argcheck(L, posi >= 1, 2, "out of range");
    luaL_argcheck(L, pose <= (lua_Integer)len, 3, "out of range");
    if (posi > pose) return 0;  /* empty interval; return no values */
    if (pose - posi >= INT_MAX)  /* (lua_Integer -> int) overflow? */
        return luaL_error(L, "string slice too long");
    n = (int)(pose -  posi) + 1;
    luaL_checkstack(L, n, "string slice too long");
    n = 0;
    se = s + pose;
    for (s += posi - 1; s < se;)
    {
        int code;
        s = utf8_decode(s, &code);
        if (s == NULL)
            return luaL_error(L, "invalid UTF-8 code");
        lua_pushinteger(L, code);
        n++;
    }
    return n;
}


static void pushutfchar(lua_State *L, int arg)
{
    lua_Integer code = luaL_checkinteger(L, arg);
    luaL_argcheck(L, 0 <= code && code <= MAXUNICODE, arg, "value out of range");
    lua_pushfstring(L, "%U", (long)code);
}


/*
** utfchar(n1, n2, ...)  -> char(n1)..char(n2)...
*/
static int utfchar(lua_State *L)
{
    int n = lua_gettop(L);  /* number of arguments */
    if (n == 1)  /* optimize common case of single char */
        pushutfchar(L, 1);
    else
    {
        int i;
        luaL_Buffer b;
        luaL_buffinit(L, &b);
        for (i = 1; i <= n; i++)
        {
            pushutfchar(L, i);
            luaL_addvalue(&b);
        }
        luaL_pushresult(&b);
    }
    return 1;
}


/*
** offset(s, n, [i])  -> index where n-th character counting from
**   position 'i' starts; 0 means character at 'i'.
*/
static int byteoffset(lua_State *L)
{
    size_t len;
    const char *s = luaL_checklstring(L, 1, &len);
    lua_Integer n  = luaL_checkinteger(L, 2);
    lua_Integer posi = (n >= 0) ? 1 : len + 1;
    posi = u_posrelat(luaL_optinteger(L, 3, posi), len);
    luaL_argcheck(L, 1 <= posi && --posi <= (lua_Integer)len, 3,
                  "position out of range");
    if (n == 0)
    {
        /* find beginning of current byte sequence */
        while (posi > 0 && iscont(s + posi)) posi--;
    }
    else
    {
        if (iscont(s + posi))
            luaL_error(L, "initial position is a continuation byte");
        if (n < 0)
        {
            while (n < 0 && posi > 0)    /* move back */
            {
                do    /* find beginning of previous character */
                {
                    posi--;
                }
                while (posi > 0 && iscont(s + posi));
                n++;
            }
        }
        else
        {
            n--;  /* do not move for 1st character */
            while (n > 0 && posi < (lua_Integer)len)
            {
                do    /* find beginning of next character */
                {
                    posi++;
                }
                while (iscont(s + posi));    /* (cannot pass final '\0') */
                n--;
            }
        }
    }
    if (n == 0)  /* did it find given character? */
        lua_pushinteger(L, posi + 1);
    else  /* no such character */
        lua_pushnil(L);
    return 1;
}


static int iter_aux(lua_State *L)
{
    size_t len;
    const char *s = luaL_checklstring(L, 1, &len);
    lua_Integer n = lua_tointeger(L, 2) - 1;
    if (n < 0)  /* first iteration? */
        n = 0;  /* start from here */
    else if (n < (lua_Integer)len)
    {
        n++;  /* skip current byte */
        while (iscont(s + n)) n++;  /* and its continuations */
    }
    if (n >= (lua_Integer)len)
        return 0;  /* no more codepoints */
    else
    {
        int code;
        const char *next = utf8_decode(s + n, &code);
        if (next == NULL || iscont(next))
            return luaL_error(L, "invalid UTF-8 code");
        lua_pushinteger(L, n + 1);
        lua_pushinteger(L, code);
        return 2;
    }
}


static int iter_codes(lua_State *L)
{
    luaL_checkstring(L, 1);
    lua_pushcfunction(L, iter_aux);
    lua_pushvalue(L, 1);
    lua_pushinteger(L, 0);
    return 3;
}


/* pattern to match a single UTF-8 character */
#define UTF8PATT    "[\0-\x7F\xC2-\xF4][\x80-\xBF]*"


static const luaL_Reg funcs[] =
{
    {"offset", byteoffset},
    {"codepoint", codepoint},
    {"char", utfchar},
    {"len", utflen},
    {"codes", iter_codes},
    /* placeholders */
    {"charpattern", NULL},
    {NULL, NULL}
};


LUAMOD_API int luaopen_utf8(lua_State *L)
{
    luaL_newlib(L, funcs);
    lua_pushlstring(L, UTF8PATT, sizeof(UTF8PATT) / sizeof(char) - 1);
    lua_setfield(L, -2, "charpattern");
    return 1;
}

